/*
 * Copyright (C) 2011 Whisper Systems
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.thoughtcrime.redphone.crypto;

/**
 * A class for managing RTP sequence numbers, wraparound, etc.
 * Extends shorts lowly changing 16bit sequence ids into long 64bit sequence ids, to avoid wraparound.
 *
 * @author Craig Gidney
 * @author Moxie Marlinspike
 *
 */

public class SequenceCounter {
  private long curLongId;
  public long convertNext(short nextShortId) {
    short smallestDeltaToCongruentId = (short)(nextShortId - curLongId); 
    curLongId += smallestDeltaToCongruentId;
    return curLongId;
  }
  public void updateSequence(SecureRtpPacket packet) {
    packet.setLogicalSequence(convertNext((short)packet.getSequenceNumber()));
  }
}
